(C) 4
(D) 5
(E) 6
Fortunately, these questions are easy to answer if you use the “plug-in”
balancing strategy. Start with choice A, and put the number 1 in front of CO 2.
(Don’t be afraid to write in your test booklet as much as you want. Your test
booklet belongs to you, and nobody cares what you write in it; only your answer
sheet is scored.) By adding a 1 in front of CO 2 , we end up with 1 carbon on the
right. Yet, we have at least 2 carbons on the left, so we know that 1 is not the
answer.
Let’s try choice B. Put a 2 in front of CO 2 , and see what happens. We have 2
carbons on the right and 2 on the left. Good. We have 4 hydrogens on the left, so
let’s try putting a 2 in front of the H 2 O. That gives us a total of 6 oxygens on the
right and 2 on the left. Let’s put a 3 in front of O 2 on the left, so we have a total
of 6 oxygens on the left.
Now we have 2 carbons on the right and the left, 4 hydrogens on the right and
the left, and 6 oxygens on the right and the left. The equation is balanced, and B
is correct. So, every time a question asks you to balance an equation, use the
plugging-in strategy. It can’t fail.